zhǐyào / zhīdào / yuán / de / zhíjìng / jiù / kěyǐ / jièzhù / yuánzhōulǜ / gūsuàn / tā / de / zhōucháng

只要知道圆的直径，就可以借助圆周率估算它的周长。

As long as you know the diameter of a circle, you can use pi to estimate its circumference.